1. Field of the Invention
The present invention relates to filter screens used in downhole drilling technologies in the oil and gas industry.
2. Description of the Related Art
In the oil and gas industry, downhole drilling operations may drill boreholes that extend thousands of feet into the ground. A fluid called drilling mud is used to facilitate drilling. As shown in FIG. 1, drilling mud circulates through the drilling system. Mud pumps 110 pump the mud from mud tanks 105 located at the surface. The mud gets pumped through the kelly hose 115 and the top drive 120. The mud is further pumped through the drill string, or drill pipe, 125 to the bottom hole assembly 130. As it reaches the bottom of the borehole, the mud acts to cool and clean the drill bit 135. The mud also picks up rock formation cuttings and circulates them back up through the annulus 140 between the drill string and casing back through the blowout preventers 145 to the surface. At this point, the mud gets processed through a shale shaker 150 before returning to mud tanks 105 to start the process of being pumped downhole again.
As the mud circulates through this system, it may pick up significant amounts of debris, which can affect the flow of the mud and the operation of the drill bit and other tools. A filter screen subassembly may be installed in the drill string to help collect and filter debris. Downhole filter screens are often run during directional drilling and are typically installed near the drill bit at the bottom of the drill string, and thus are not easily accessible during drilling. To remove or clean out a downhole filter screen, the entire drill string must be pulled out of the wellbore. Downhole filter screens typically employ flanges to be secured in a section of drill string. The flanges necessitate the insertion and removal of the existing filter screens from the box end (i.e., uppermost end) of a drill string section.
Additionally, downhole filter screens are easily damaged during drilling operations. If a filter screen fills with debris and is not properly maintained or cleaned, then it can cause blockages in the fluid flow or potentially “wash out.” In other words, the filter screen may shear off due to excess debris buildup or excess vibration during drilling operations. The broken filter screen can be pushed by the fluid flow of the drilling mud and may end up at the bottom of the borehole. Due to the inconveniences from factors such as installation, cleaning, and maintenance, filter screens are often not used by drilling operators despite the benefits they provide in filtering drilling mud.
Surface pipe screens are also sometimes used to filter drilling mud. These pipe screens are installed in the drill string above the surface at the drilling rig, and they are designed to catch finer particulates than downhole filter screens. However, they are typically not built as robustly as downhole filter screens and require constant maintenance. They typically installed at the box end of a pipe segment and are held in place using a flange. Surface pipe screens also require constant maintenance. Each time a new drill pipe segment is ready to be added to the drill string, the top drive must be disconnected from the drill string. Before connecting the new drill pipe segment, the installed surface pipe screen must be removed from the topmost exposed segment (i.e., box end) of drill pipe in the drill string. After the new drill pipe segment is connected to the drill string, the surface pipe screen can be reinstalled into the new drill pipe segment's box end, and the top drive can be reconnected with the drill string. If the surface pipe screen is ever forgotten when adding new segments of pipe, the surface pipe screen may become “lost” in the drill string, making its retrieval difficult and tedious. Further, if a surface pipe screen ever shears off, it may become lodged along with debris anywhere in the drill string.
Additionally, surface pipe screens can present safety issues. Many drilling operators enforce a safety zone around the drill string when the top drive is disconnected from the drill string because it is a pinch point. Many operators forgo the use of surface pipe screens, rather than risk the safety of personnel during the frequent insertion and removal of a surface pipe screen during drilling operations.
Accordingly, there exists a need for the safe and easy attachment and removal of a filter screen that is constantly positioned at the surface of a drilling rig.